in 4 gear but at a lower speed of course it depends on a lot of conditions my mileage was higher as i went slower down to 47mph. not realistic driving that works on a highway. get yourself a scangauge2 unit and once setup. get on some flat road on drive your various speed you are comfortable with and pay attention to the avg mph, instant mpg( which changes more rapidly then the average mpg) and gallons per hour reading to find your sweet spot. it will take into account how your specific setup is working for you. makes for a nice code reader and trip computer(also helps getting the most from gas) as well. costs about $160 but they make others to suit your needs.